1. Field of the Invention
The present invention relates to a silent chain which is constructed to reduce noises generated when meshing with a sprocket and to improve the lifetime of the chain.
2. Description of the Related Art
Silent chains are used extensively for a variety of purposes, such as power transmission between an engine crank-shaft and a camshaft in an automotive vehicle. These silent chains include a plurality of rows of link plates serially interconnected or articulated with each other, and each of the link plates is in a virtually bifurcated or V shape to provide, at its opposite ends, a pair of meshing teeth which are directly meshable with successive teeth of a sprocket wheel. More specifically, outside or inside flanks of these teeth are sequentially brought into a power-transmitting contact with the sprocket teeth.
FIG. 5 shows one example of the conventional silent chains which is disclosed in Japanese Patent Publication No. HEI-1-56304. The disclosed silent chain 50, for the purpose of reducing an impact and noises during power-transmitting meshing operation thereof, includes an inside flank 52 of arcuate convex profile and an outside flank 54 of straight profile which jointly form each tooth 56 of one link plate. When the silent chain 50 is in a straight-line state, the arcuately convex inside flank 52 of one link plate projects outwardly from the straight outside flank 54 of the preceding link plate.
FIG. 5 also illustrates an operational sequence in which the link plates of the silent chain 50 sequentially mesh with teeth of a sprocket S. At the onset of meshing engagement between the link plates of the silent chain 50 and the teeth of the sprocket S, the arcuate convex inside flanks 52 of the link plate are caused to interfere with and then slide along the sprocket teeth, as achieved at the position of a tooth T1 of the sprocket S. When the link plates of the silent chain 50 are placed in full meshing engagement with the sprocket teeth, the straight outer flanks 54 of the link plates are completely seated on the sprocket teeth, as achieved at the position of another tooth T2 of the sprocket S. By the meshing engagement between the outside flanks 54 of the link plates and sprocket teeth thus acheived, the silent chain achieves its power-transmitting operation between, for example, a crankshaft and a camshaft in an engine.
In the case of the link plates having the combination of an arcuate convex inside flank 52 and a straight outside flank 54, a problem arises in that the projecting length of the arcuately convex inside flank 52 becomes excessively large at a central portion of the inside flank 52, thereby hindering smooth intermeshing engagement between the silent chain 50 and the sprocket S. If the projecting length at the central portion of the arcuate convex inside flank 52 is made small, a sufficient noise-suppressing effect cannot be attained partly due to insufficient interference between the inside flank 52 and the sprocket tooth occurring in the vicinity of a tip of each tooth of the link plate, and partly due to a delay in timing of the meshing operation.
In addition, due to the excessive projectina length at the central portion of the arcuately convex inside flank 52, wear of the inside flanks 52 and the sprocket tooth occurs in a relatively short time, making it difficult to maintain the prescribed noise-suppressing effect of the silent chain.